maddy

 1/*
 2Maddy Mail Server - Composable all-in-one email server.
 3Copyright © 2019-2020 Max Mazurov <fox.cpp@disroot.org>, Maddy Mail Server contributors
 4
 5This program is free software: you can redistribute it and/or modify
 6it under the terms of the GNU General Public License as published by
 7the Free Software Foundation, either version 3 of the License, or
 8(at your option) any later version.
 9
10This program is distributed in the hope that it will be useful,
11but WITHOUT ANY WARRANTY; without even the implied warranty of
12MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
13GNU General Public License for more details.
14
15You should have received a copy of the GNU General Public License
16along with this program.  If not, see <https://www.gnu.org/licenses/>.
17*/
18
19package limiters
20
21import "context"
22
23// Semaphore is a convenience wrapper for a channel that implements
24// semaphore-kind synchronization.
25//
26// If the argument given to the NewSemaphore is negative or zero,
27// all methods are no-op.
28type Semaphore struct {
29	c chan struct{}
30}
31
32func NewSemaphore(max int) Semaphore {
33	return Semaphore{c: make(chan struct{}, max)}
34}
35
36func (s Semaphore) Take() bool {
37	if cap(s.c) <= 0 {
38		return true
39	}
40	s.c <- struct{}{}
41	return true
42}
43
44func (s Semaphore) TakeContext(ctx context.Context) error {
45	if cap(s.c) <= 0 {
46		return nil
47	}
48	select {
49	case s.c <- struct{}{}:
50		return nil
51	case <-ctx.Done():
52		return ctx.Err()
53	}
54}
55
56func (s Semaphore) Release() {
57	if cap(s.c) <= 0 {
58		return
59	}
60	select {
61	case <-s.c:
62	default:
63		panic("limiters: mismatched Release call")
64	}
65}
66
67func (s Semaphore) Close() {
68}